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// ---
// Author: Jeffrey Junfeng Pan (panjunfeng@gmail.com)

// This is an abstract class for accessing transactions sequentially.
// Transactions can be stored in memory or in files without loading
// them to memory. You can implement your own version for accessing
// transactions. The frequent pattern mining algorithm only needs to
// access all data sequentially. So your implementation should be
// optimized for that.
//
// Example of implementation:
// 1) class TransactionsMemoryImpl (see transactions_file_impl.h):
//      stores all transactions in memory as vectors.
// 2) class TransactionsFileImpl (see transactions_memory_impl.h):
//      stores all transactions in file without loading the whole to
//      memory. It allows the algorithm to process relatively
//      large number of transactions.
//
// Implementation shall consider:
// 1) optimize for sequential reading: operator[] and operator()
// 2) size() is only called after a full scan of transactions.
//    It is ok if size is not known beforehand.

#ifndef FP_GROWTH_TRANSACTIONS_H_
#define FP_GROWTH_TRANSACTIONS_H_

#include <vector>

#include "base.h"
#include "common/macros.h"

namespace frequent_pattern_mining {

// ------------------------------------------------------------
//                      Declaration
// ------------------------------------------------------------

template <typename T>
class Transactions {
 public:
  // Constructor.
  Transactions() {}

  // Destructor.
  virtual ~Transactions() {}

  // Return the size of transactions.
  // The size is NOT weighted by transaction frequencies.
  // Each transaction counts 1.
  virtual int size() = 0;

  // If there is no transaction at all.
  virtual bool empty() = 0;

  // Return the transaction given the index.
  // The implementation shall optimize for sequential reading.
  virtual vector<T>& operator[](int index) = 0;

  // Return the frequency given the index.
  virtual int operator()(int index) = 0;

  // Whether or not the transaction exists given the index.
  virtual bool is_valid(int index) = 0;

 private:
  DISALLOW_EVIL_CONSTRUCTORS(Transactions);
};

}  // namespace frequent_pattern_mining

#endif  // FP_GROWTH_TRANSACTIONS_H_
